Process for crystallizing bis(beta-hydroxyethyl)terephthalate

ABSTRACT

A PROCESS FOR PURIFYING BIS(B-HYDROXYETHYL)TEREPHTHALATE BY CRYSTALLIZATION IN WHICH CRYSTAL MODIFYING AGENTS ARE ADDED TO SOLUTIONS OF THE ESTER TO INDUCE FORMATION OF CRYSTALS OF A SIZE AND SHAPE THAT PERMITS THEIR RECOVERY FROM THE SOLUTION IN PURE STATE.

United States Patent 3,577,454 PROCESS FOR CRYSTALLIZING BIS(B-HYDROXY-ETHYL)'I'EREPHTHALATE Max H. Keck, Cuyahoga Falls, Ohio, assignor to TheGoodyear Tire & Rubber Company, Akron, Ohio No Drawing. Filed July 1,1968, Ser. No. 741,312 Int. Cl. C07c 69/82 U.S. Cl. 260-475 4 ClaimsABSTRACT OF THE DISCLOSURE A process for purifying bis(fi-hydroxyethyDterephthalate by crystallization in which crystalmodifying agents are added to solutions of the ester to induce formationof crystals of a size and shape that permits their recovery from thesolution in pure state.

This invention relates to the purification ofbis(fl-hydroxyethyl)terephthalate. More particularly the inventionrelates to an improved method of crystallizingbis(;3-hydroxyethyl)terephthalate and recovering the material fromsolution.

BisQS-hydroxyethyl)terephthalate can be prepared by reactingterephthalic acid with ethylene glycol. It can also be formed by thedepolymerization of preformed polyester resin by treatment of the resinwith an excess of ethylene glycol according to methods known in theprior art. The product resulting from depolymerization of polyethyleneterephthalate with ethylene glycol is primarilybis(;8-hydroxyethyl)terephthalate and small amounts of the dimer ofbis(fi-hydroxyethyl)terephthalate, diethylene glycol, bis(diethyleneglycol)terephthalate, oligomers and low molecular weight color bodies.The recovery of the bis(fl-hydroxyethyl)terephthalate made by suchprocesses is very difiicult because the bis(fi-hydroxyethyl)terephthalate forms a gelatinous mass with the impurities present. Itdoes not readily form sharp well-defined crystals and thus cannot berecovered by the usual filtering or centrifuging operations It is anobject of this invention to provide an improved method for crystallizingand purifying bis(/8-hydroxyethyl)terephthalate.

Now it has been found that branched chain glycol modifying agents inducebis([3-hydroxyethyl)terephthalate to form well-defined crystals andgreatly improve the filterability of the crystalline mass obtained frommixtures of bis(fl-hydroxyethyl)terephthalate with its dimer, trimer,and other impurities obtained in the deploymerization of resin withglycol.

The branched chain glycol modifying agents of this invention arecompounds of the formula:

wherein R1 can b H, CH3, C2H5, C3H7, C4H9, C5H11, cyclohexyl or phenyland R can be CH C H C H C H C H cyclohexyl or phenyl.

The process of this invention includes the crystallization ofbis(/8-hydroxyethyl)terephthalate by the addition of a branched chainmodifying agent to mixtures of this material so that separation of thebis(, 3'hydroxyethyl) terephthalate can be accomplished whereas withoutthe addition of the branched chain modifying agent the mixture oncrystallization will not permit the separation of bis(3-hydroxyethyl)terephthalate. This is meant to include the separation ofthe bis ester when it is prepared 'by reaction of terephthalic acid andethylene glycol and 3,577,454 Patented May 4, 1971 "Ice EXAMPLE I A gramquantity of polyethylene terephthalate polymer, 300 cc. of ethyleneglycol and 4 grams of 2-ethyl-2-butyl-1,3-propanediol were placed in a1-liter 3-neck flask fitted with thermometer, stirrer andrefluxcondenser. The mixture was heated and stirred at reflux for threehours at which time a clear solution was obtained. This solution wastransferred to a beaker and diluted with an additional 200 cc. ofglycol. The mixture was then cooled slowly with slow stirring. A mass ofcrystals formed. The crystals thus obtained were readily filtered onto aBuchner funnel. A rubber dam was used to squeeze out as much of theliquid phase as possible. The damp filter cake was then suspended in cc.of fresh glycol, gently stirred and again filtered and squeezed fairlydry on the funnel by means of the rubber dam. The damp yield weighed 200grams. A portion of this product was polymerized by the regularcondensation method at 280 C. and 0.20 millimeters of mercury pressurein the presence of manganese acetate and antimony oxide as catalyst. Ahigh molecular weight polymer of good color was formed. The differentialthermal analyzer melting point of this polymer was 253 C. This indicatedthat the bis(Bhydroxyethyl)terephthalate was ,of good quality and thatonly a very small amount of impurities such as diethylene glycollinkages were present in the polyester chain.

EXAMPLE II A 100 gram quantity of polyethylene terephthalate polymer wasdepolymerized as described in Example I except that no modifying agentwas used. The mass obtained on cooling the reaction mixture was a slurryof a gelatinous character which could not be vacuum filtered. Pressurefiltration was also unsatisfactory because the filter became clogged andthe throughput of filtrate was extremely slow. A small amount of thesolid material which was isolated by pressure filtration was polymerizedand the resulting polymer had a Differential Thermal Analyzer meltingpoint of only 237 C. indicating the presence of a high level ofimpurities in the recovered bis(fi-hydroxyethyl)terephthalate.

EXAMPLE III A 4 lb. quantity of polyethylene terephthalate, 4 lbs. ofethylene glycol and 0.16 lb. of 2-ethyl-2-butyl-l,3-propanediol wasplaced in a stainless steel reactor. The mixture was stirred and heatedat 220 C. at 20 lbs. per square inch pressure for 3 /2 hours. A clearsolution resulted. An additional 10 lbs. of ethylene glycol were addedto dilute the reaction mixture and the reaction mixture was then allowedto cool while slowly stirring. The crystals formed were recovered byfiltration under vacuum. Filtration took place with ease and rapidly. Asmall sample of the damp filter cake was polymerized to provide apolymer of excellent color, high molecular weight, and a DifferentialThermal Analyzer melting point of 254 C.

The above melting point value is identical to that obtained bypolymerizing a sample of pure bis(B-hydroxy ethyl)terephthalate whichhad been prepared by the reaction of terephthalic acid and ethyleneoxide.

The invention has been described with respect to the purification of bis(B-hydroxyethyl)terephthalate from depolymerized polyethyleneterephthalate. The invention is equally applicable to the purificationof his (fi'hydroxyethyl) terephthalate produced by other means includingthe reaction of terephthalic acid and ethylene glycol. The invention isalso applicable to copolyrners containing at least 85% ethyleneterephthalate.

The invention has been described with respect to the use of 2ethyl-2-butyl-1,3-propanediol 'as the branched chain modifying agent.Other branched chain modifying agents that can be used in addition to2-ethyl-2-butyl-1,3- propanediol include 2,2-diethyl 1,3 propanediol;2,2-dimethyl-l,3-propanediol; 2,2-diphenyl-1,3-propanediol; 2-methyl-Z-propyl-1,3-propanediol; 2-ethyl 2 phenyl-1,3- propanediol; 2cyclohexyl 2 ethyl-1,3-propanediol; 2-cyclohexyl-1,3-propanediol and2-amyl-l,3-propanediol.

The branched chain modifying agents are used in the range of from about1% to about 7% by weight based on the Weight of polymer beingdepolymerized or Weight of bis(;8-hydroxyethyl)terephthalate beingpurified. The preferred range of concentration for the branched chainmodifying agent is 2 to 4% by weight based on the Weight of polymerbeing depolymerized or weight of bis(;8-hydroxyethyl)terephthalate beingpurified.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

1. The process of purifying bis(,8-hydroxyethyl)terephthalate preparedby depolymerizing a polymeric polyethylene terephthalate resin with anexcess of ethylene glycol or by reacting terephthalic acid with ethyleneglycol which comprises crystallizing saidbis(fl-hydroxyethyl)terephthal'ate from ethylene glycol in the presenceof a branched chain glycol having the formula 4 wherein R can be H, Ch CH C l-I C H C H cyclohexyl or phenyl and R can be CH C H C3H7, C H C Hcyclohexyl or phenyl, and recovering thebis([3-hydroxyethyl)terephthalate.

2. The process of claim 1 in which the branched chain glycol modifyingagent is selected from 2-ethyl-2-butyl- 1,3-propanediol; 2,2 diethyl1,3-propanediol; 2,2-dimethyl-1,3-pr0panediol; 2,2 diphenyl1,3-propanediol; 2methy1-2-propyl-1,3-propanediol; 2 ethyl-2-phenyl-l,3-propanediol; 2 cyclohexyl 2-ethyl-l,3-propanediol; 2- cyclohexyl1,3-propanedio1 and 2-amyll,3-propanediol.

3. The process which comprises depolymerizing polymeric ethyleneterephthalate resin with an excess of ethylene glycol and crystallizingthe bis(fi-hydroxyethyl) terephthalate formed from ethylene glycolcontaining from 1 to 7 percent by weight based on the weight of thebis(;8-hydroxyethyl)terephthalate of a branched chain glycol having theformula RI HOGHzC JCHzOH ls wherein R can be H, CH C H C H C H C Hcyclohexyl or phenyl and R can be CH C H C3H7, C H C H cyclohexyl orphenyl.

4. The process of claim 3 whereby the branched chain modifying agent is2-ethyl-2-butyl-1,3-propanediol.

References Cited UNITED STATES PATENTS 3,268,575 8/1966 Keck 260-475 5CHARLES B. PARKER, Primary Examiner E. J. SKELLY, Assistant Examiner

